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Whoever Satoshi was he didn't invent Bitcoin alone. It was a collaboration between Satoshi, Hal Finney and Ray Dillinger building on the previous work of Adam Back and others.
I wonder how much of it was derived from Hal's work on RPOW?
To bad we can't ask them. Two out of the three are gone.

Well, you can ask Ray whatever you want. He's active here.
Uhh, I don't remember ever agreeing to keep it secret, but we didn't talk about it on the list either. At that time Hal was elbows-deep in the transaction scripting code, and I was checking Satoshi's work on the crypto on the blockchain architecture.
Finney had a lot to worry about with the transaction scripting and wound up blocking out about a dozen more opcodes than Satoshi had wanted to, but I found essentially nothing wrong with the block structure. I am still freakin' amazed how tight he got that blockchain design.
And, yeah, I'm Ray Dillinger.